There has been considerable development over the last twenty years in the design and manufacture of repositionable adhesives, specifically in methods of making inherently tacky, elastomeric, solvent insoluble, solvent dispersible polymeric microspheres. These microspheres, either solid or hollow, are typically combined with appropriate binders and thickening agents to form adhesives which are coated by various methods on backing materials such as papers, films and foils.
Inherently tacky acrylic microspheres utilized in these adhesive compositions are produced by suspension polymerization methods which have become quite common. In all of these techniques surfactants are used to stabilize the microspheres in the suspension polymerization process. Following the polymerization process, additional wetting agents or surfactants are often added to increase the wetting ability of the microsphere composition on support surfaces. For example, Tsujimoto Patent WO97/14510 describes a transfer coatable water based microsphere adhesive composition for sheet-to-sheet coating processes. It teaches that a surfactant, in addition to surfactant within the polymeric microsphere composition itself and its binders and thickening agents, is added during the manufacture of the adhesive composition to enhance wetting on a silicon surface. This is a well known practice.
However, the addition of wetting agents or surfactants to microsphere compositions in adhesive manufacture is not without disadvantages. The wetting agent or surfactant may migrate from the finished product if present in excessive amounts. In transfer coating processes, the tack and peel of the adhesive microsphere compositions can be diminished by wetting agents or surfactants in too great an amount. Also, typical wetting agents such as fluorosurfactants and specialty diols are quite expensive.
It is the purpose of the present invention to improve upon methods of making repositionable pressure sensitive adhesives in a manner such that surfactants are not added to the microsphere compositions as in the Tsujimoto reference and those surfactants present in the microsphere composition or its binders or thickening agents are significantly reduced. By achieving these objects, migration of wetting agent from the finished products is greatly lessened if not eliminated, the inherent tack and peel of the adhesive microsphere compositions are increased and use of expensive added wetting agents such as fluorosurfactants and specialty diols is avoided.